Z3 6 



^ o 





8S 





DRYLAND FARMING. 



Perfectly dry soil. 



343 



Hygroscopic Coefficient. 

 'VViltiiifr Coefficient. 



O 



Optimum moisture content for ordinary crops. 



■Maximum capillary capacity. 



Completely saturated soil. 



Water is lost to plants through the agencies of transpira- 

 tion, evaporation, run-off, and percolation. 



(1) Transpiration Eatio or the Water Kequirements 

 OF Plants. — During the elaboration of plant structures, while 

 a comparatievly small and practically negligible quantity of 

 water enters into its composition, very large quantities are 

 transpired through the plant. The transpiration ratio is de- 

 fined as the quantity of water in pounds required to produce 

 one pound of dry matter, or the ratio of the total water trans- 

 pired to the total weight of dry matter produced in the crops. 

 This ratio is affected by many conditions, chief among which 

 are the average humidity, the fertility of the soil, and the kind 

 of crop grown. 



